Within many industries and the oil industry in particular, oily soils, sludges and emulsions may be produced at various times throughout the regular operations or processes employed within the sector. Increasing environmental awareness and more stringent environmental regulation has necessitated the more frequent movement, handling, and treatment of such wastes and more sophisticated and environmentally benign methods of disposal.
Historically, many such wastes were either disposed of directly into the receiving environment in either a controlled or an uncontrolled manner or stored in pits, lagoons or ponds where natural seepage and evaporation reduced the level of liquids leaving viscous solids and sludge residues. Alternatively such wastes may have been incorporated in landfills, pumped into disused mine shafts and salt mines, or injected into old oil wells as a solution to finally dispose of the materials from the generation site location.
Oily wastes from within the oil industry occur at numerous stages from the drilling phase through to the delivery of consumer products. At the well drilling phase the use of “oils” in drilling fluids is often encountered, particularly when the drilling of water sensitive formations or directional drilling is required. The “oil” may be used either as an additive to the aqueous based drilling fluid (generally termed as muds) or as the base of the drilling fluid such as in oil-based mud (OBM) or invert oil emulsion mud (IDEM). The “oil” used within mud encompasses a range of materials as the hydrophobic fraction. Crude oils, fuel fractions (such as diesel or kerosene), white oils, esters, selected olefins, acetals and many other materials have all been used within muds either as the liquid base of the mud or as an additive to the mud. The use of such muds can result in the generation of considerable quantities of oil contaminated drilled material removed from the well (referred to within the industry as waste drill mud cuttings or cuttings). These contaminated cuttings materials were frequently disposed of off site spreading in both land and marine environments or transported to landfill sites, possibly with some intermediate oil reduction or stabilisation phase. Within the industry literature, there are numerous references to cuttings cleaning equipment and several devices for oil reduction of cuttings have been patented. In the late 1980's, the use of subterranean injection into well annuli became popular with the first process being patented by the ARCO oil company (now incorporated within BP). Several other patents exist for such equipment based on different cominution technologies (such as wet autogenous grinding and ultrasonics).
One major current method of transportation is known as “skip and ship” whereby the wastes are loaded into containers or skips. These are then lifted by crane to waiting vessels, and the containers are transported back to shore for offloading at the dockside. However, there are problems associated with this method especially concerning the significant logistics involved. Suitable deck space is required both on the operating platform and on the transport vessel to accommodate the skips. The required lifting apparatus must be present along with the personnel to operate such equipment. In addition, there are considerable health and safety risks involved when moving large quantities of this kind of equipment under sea faring conditions in relatively short time periods. The same disadvantages are also encountered at the dockyard for the tasks of unloading to treatment and disposal sites. Also when at sea such operations are limited by the weather conditions and these operations must be put on hold when weather conditions become more severe. This may result in significant downtime and lost revenues.
Alternatives to this method of transportation have been designed to eradicate the use of skips and the movement thereof. Many of these alternative transport methods require and rely on the homogenization and slurrification of these essentially solid oil contaminated wastes in order to enable and facilitate pumping methods and techniques. The processed wastes are then pumped direct through piping mechanisms to containers or holds on waiting shipping vessels. Similar operations then take place at the quayside for unloading. This allows the ability to process and transport the cuttings as they are produced in drilling operations whilst using minimal deck space and whilst avoiding the use of lifting engineering equipment and personnel therefore operations are less hampered by prevailing weather conditions.
Cuttings are also often moved between sites for disposal by either vacuum truck or in tanks and containers. The irregular nature of the drilled rock particles and the in-built viscosity of the drilling fluids poses significant handling problems for all of the above processes and it is common for other fluids such as muds, water and oil to be added to increase the ease of handling. This can considerably increase the amount of materials that need to be treated or disposed of, increases the volumes that may be required to be transported, and can incur additional costs for the dilution fluid, especially if they are oils or muds.
In the production of oil and gas solids may be produced with the hydrocarbons which can settle in vessels and tanks. Removal of such materials may be by manual application, vacuum suction or sludge pumps. Dilution, usually in the form of water is common to mobilise the settled materials whilst oils may often be used to facilitate the dissolution of the heavier ends of the oil to aid in mobilisation of the material so that pumps may be used. The addition of other extraneous liquid again increases the volumes of wastes to be handled and treated/disposed of. In addition, the use of hydrocarbon oils complicates the operations in terms of fire/explosion protection and the protection of operators from exposure to vapours that may be carcinogenic or otherwise hazardous to health.
Emulsions may also be formed within tanks vessels or collection ponds or lagoons that require removal, treatment and/or disposal. These may be of considerable viscosity and contain low to moderate levels or particulate or waxy material precipitated from the oil. Similar materials may also occur after oil spills at sea. These materials may be oil continuous, but contain up to 80% water. Moreover, in general water added to reduce viscosity can exhibit a hydrating effect in the presence of oil-contaminated shales and the like resulting in an extremely high viscosity or indeed a congealed material. The viscosity of both the oil spill and production emulsions can be several hundreds of thousands of centipoises, making them virtually impossible to pump other than by very specialist equipment. Consequently, dilution may be used to facilitate pumping by a wider range of units.